Ceramic Matrix Composite (CMC) materials may be used in aerospace engine applications because of their mechanical properties and chemical stability at high temperature. Turbine bladetrack, vanes, and blades of gas turbine engines may be manufactured from CMC materials.
Coupling together two or more components made of CMC material may be difficult for a number of reasons. One reason coupling is difficult is that coupling alloys including nickel and/or gold may exhibit melting temperatures below about 1200° C. As a result, joints brazed with nickel and/or gold alloys have very low or no mechanical strength and oxidation resistance at temperatures above about 1250° C. Another reason coupling may be difficult is that nickel and/or gold-based braze alloys may have a tendency to form low melting eutectic phases in braze joints and the areas adjacent the braze joints due to CMCs often containing some free silicon. The eutectic phases develop from braze alloy interaction. For example, the gold-based braze alloy may be problematic as it would form a low temperature eutectic phase, for example, gold-silicon eutectic phase, that has a melting temperature of about 360° C. The resulting braze joint and surrounding areas may then be susceptible to failure and oxidation at high temperatures. As a result, such braze joints may not be suitable in high temperature sections of gas turbine engines.
In addition, CMC materials may be brittle and have much lower Coefficients of Thermal Expansion (CTE) than those of most conventional braze filler metals. The high temperature brazing process could produce significant thermal residual stresses in the braze joints. The thermal residual stresses can cause, for example, CMC or joint cracking during the cooling cycle or in service.